In a manufacturing process of a semiconductor device, for making a substrate surface clean, cleaning processing of processing a substrate using cleaning liquid is performed by eliminating part of films on the substrate and forming a desired pattern, or eliminating all of the films. As processing devices that perform such cleaning processing, there are known a single-wafer-type device that cleans substrates one by one, and a batch-type device that cleans a plurality of substrates by soaking the plurality of substrates in processing liquid in a processing bath in a state in which the plurality of substrates are held at predetermined intervals (e.g., Patent Literature 1).
In addition, in a manufacturing process of a semiconductor device, out of a silicon nitride film (Si3N4 film) and a silicon dioxide film (SiO2 film) that are formed on a substrate such as a silicon wafer, the silicon nitride film is often selectively eliminated through etching performed by cleaning processing. Phosphoric acid (H3PO4) aqueous solution is often used as processing liquid for eliminating the silicon nitride film. Due to its properties, the phosphoric acid aqueous solution etches not only the silicon nitride film but also a slight amount of the silicon dioxide film. Because minute patterns are required of today's semiconductor devices, it becomes important to keep an etching rate constant for controlling an etching amount, and to keep a selection ratio, which is a ratio between respective etching rates of the silicon nitride film and the silicon dioxide film, constant.